1. Field of the Invention
The present invention relates to an image pickup apparatus, more particularly, although not exclusively, to an image pickup apparatus configured to switch photographing between a color-photographing mode and a black and white (“black & white”) photographing mode.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2001-45512 discusses a conventional image pickup apparatus capable of switching the photographing modes from the color photographing mode to the black & white photographing mode and vice versa. This type of conventional image pickup apparatus uses CCDs as image pickup elements, and during the color photographing mode, an infrared ray cutoff filter is disposed in front of the CCDs, in order to improve the reproducability of the color in the visible rays band. Further, during the black & white photographing mode, such a configuration is used in which an infrared ray cutoff filter is removed so as to increase the quantity of light. In the described image pickup apparatus, a so-called hunting operation is reduced, which is the repeatedly switching of the image mode between the color and the black & white photographing modes. This configuration sets a plurality of threshold values of luminescence level at the time when the color photographing mode is changed over to the black & white photographing mode and also at the time when the black & white photographing mode is changed over to the color photographing mode.
With the configuration as discussed in the Japanese Unexamined Patent Publication No. 2001-45512, it is difficult to set the threshold value for the luminescence level during the black & white photographing mode for the reason that there are many different cases where the photography is carried out under the sun light, under the lightening by an incandescent lamp or a fluorescent lamp, or under the lightening by the infrared ray. Hence, problems occur in which the hunting cannot be completely prevented and the smooth switching, from the black & white photographing mode to the color photographing mode, may be reduced.
In order to address the above-mentioned problem, Japanese Unexamined Patent Publication No. 2003-219254 discusses a configuration such that switching from the black & white photographing mode to the color photographing mode is executed by taking into consideration color signals in addition to luminance signals of CCDs.
In the configuration adopted by the Japanese Unexamined Patent Publication No. 2003-219254, during the black & white photographing mode, monitoring as to whether or not the gains of respective color signals of the CCDs are equal to one another is performed to determine whether or not an increase in the luminescence level due to the infrared ray occurs. Thus, when photography is performed at a site where the wall face thereof and/or the floor face thereof is covered with a relatively lot of mono-tone color such as a green or a blue, under the lighting of the incandescent lamp, the gains of respective color signals of the CCDs become equal to each other, and as a result, the lighting is determined such that there is an occurrence of an increase in the luminescence level due to the infrared ray lighting. Accordingly, even if there is a lot of visible light, enough for implementing the color photography, the switching from the black & white photographing mode to the color photographing mode does not easily occur.
Further, Japanese Unexamined Patent Publication No. 07-284111 discusses a configuration such that an infrared ray cutoff filter is disposed in front of CCDs during the color photographing mode and a visible light cut-off filter is instead disposed during the black & white photographing mode. In this configuration, image signals from the CCDs are compared with outputs from light-receiving elements directly receiving light reflected from a photographed object to execute switching of the photographing modes between the color photographing mode to the black & white photographing mode and vice versa. At this time, in order to compensate for a differential between the focal point of the visible light and that of the infrared ray, a lens driving device is employed for adjustably moving a focussing lens along an optical axis.
In the configuration of Japanese Unexamined Patent Publication No. 07-284111, the visible light is cut by the visible light cutoff filter at the time of black & white photographing mode. Therefore, this configuration is inexpedient from the viewpoint of effective use of any quantity of light and moreover, it suffers in that a lens moving mechanism is used for the focussing lens that adjustably compensates for the focal point difference between the visible light and the infrared ray according to the switching of the photographing mode from the color to black & white photographing mode and vice versa, resulting in the entire apparatus and system becoming more complicated.